1. Field of the Invention
Nitric oxide is a short lived radical and has recently been found to be produced by various mammalian cells e.g., endothelial cells, macrophages and nerve cells. It influences the blood pressure, is a neurotransmitter and a tool of the immune response.
The detection and evaluation of the nitric oxide (NO) can be performed in different ways.
2. Related Art
The state of art shows different methods for detecting nitric oxide, for example as a color complex using sulfanile acid (Bell, F. K., O'Neill, J. J., Burgison, R. M., J. Pharm. Sci., 1963, 52, 637-639) (diazotation with NO and coupling with N (1-naphthyldiamine)), or with oxyhemoglobin (Doyle, M. P., Hoekstra, J. W., J. Inorg. Biochem., 1981, 14, 351-358), ESR-spectroscopic (Wennhalm, A., Peterson, A-S., J. Cardiovasc. Pharmacol., 1991, 17/3, S34-S40), mass-spectroscopic (Palmer, R. M. J., Ashton, D. S., Moncada, S., Nature, 1988, 333, 664-666), with the help of spin-traps (Korth, H-G., Ingold, K. U., Sustmann, R., Groot, deH., Sies H., Angew. Chem. Int. Ed. Engl., 1992, 31/7, 891-893), electrochemical (Shibuki, K., Neuroscience Research, 1990, 9, 69-76; Taha, Z., Malinski, T., Nature, 1992, 358, 676-678) or using chemiluminescence (Downes, M. J., Edwards, M. W., Elsey, T. S., Walters, C. L. , Analyst, 1976, 101, 742-748)
The chemiluminescence method used in the present inventive method relates to the reaction of NO and ozone to NO.sub.2 * and O.sub.2. During the subsequent decay of NO.sub.2 * light of the wavelength 600-875 nm is emitted, which can be measured using a photodetector. ##STR1##
Nitric oxide is a very reactive gas, that can be easily oxidized to NO.sub.2 * (nitrite) in the presence of oxygen. For evaluating the exact amount of NO in liquids it is necessary to reduce the nitrite formed as an intermediate back to NO.
According to the current state of the art (Cox, R. D., Anal. Chem., 1980, 52, 332-335), a reaction vessel with refluxing acidic acid containing 1% sodium iodide (Nal) is used and NO/water solutions are used as standards.
The sample is introduced into the reducing medium which is purged with helium for approximately 60 sec. A valve of the NO-detector is opened and the NO is transferred into the NO detector. An alkaline cooling trap prevents that the acidic vapors contaminate the NO-detector.
This system displays the following disadvantages:
a) the reaction vessel has to be heated, PA1 b) the temperature of the reaction vessel has to be held precisely to prevent fluctuations of the ground signal, PA1 c) the hot acidic vapors have to be cooled down and afterwards the gas stream has to be fed through an alkaline cooling trap, which leads to a considerable expansion of the total volume of the device followed by a reduction of the NO concentration in the gas stream, and therefore to measurement inaccuracies. PA1 d) work intensive standard curves have to be done PA1 e) the reduction is considerably slow {.about.1 minute} (Hoffman, M. R., Menon, N. K., Bing, R. J., J. of Applied Cardiology, 1990, 5, 455-460).